This invention generally relates to a vane pump, and specifically to a vane pump employing radially pressured balanced vanes with improved durability features.
Vane pumps are commonly single acting or double acting and may be fixed or variable displacement. The invention is applicable to all types of vane pumps.
A typical fixed displacement double acting vane pump includes a plurality of vanes supported within a rotor. A shaft supported concentrically within a cam block rotates the rotor. The vanes are driven outward from the rotor into contact with an inner surface of the cam block. Each vane sweeps through two inlet regions to draw in a quantity of fluid. The quantity of fluid is trapped within a chamber defined between the vanes. The variable radius of the inner surface of the cam block with respect to the concentric shaft provides for a cyclical change in volume defined between the vanes. The change in volume generates a desired fluid flow rate. The fluid is then discharged through two discharge regions at an elevated pressure as determined by the downstream resistance.
Following each inlet arc is a pump arc for transferring the fluid from the inlet region to the discharge region and to provide a discharge to inlet seal. Following each discharge region is a seal arc that completes the discharge to inlet seal. In conventional vane pumps it is known to provide a means for balancing pressures under the vanes and over the vanes in the inlet and discharge regions to maintain contact with the inner surface of the cam block. As the rotor turns the vanes are moved through a low-pressure inlet arc of the pressure chamber, a pump arc where the leading surface of the vane is exposed to increasing pressure while a trailing surface is exposed to low pressure from the inlet. The vane further rotates through a discharge arc where pressures are essentially the same on each of the leading and trailing surfaces.
The vane also rotates through a pump arc where high pressure is exerted on the leading surface of the vane and low pressure is exerted on the trailing surface and a seal arc where low pressure is exerted on the leading surface of the vane and high pressure is exerted on the trailing surface of the vane. In the inlet arc inlet pressure is provided under the vanes, therefore in the inlet arc the vanes are radially pressure balanced. In the discharge arc discharge pressure is provided under the vanes, therefore the vanes are also radially pressure balanced in the discharge arc.
In the pump arc and the seal arc to maintain a seal between the vane tip and the cam inner surface discharge pressure is provided under the vanes. Above the vane one half of the vane is subject to discharge pressure. The vane, therefore, is radially over pressure balanced by a factor of two. This excess radial pressure load results in high adhesive wear stresses between the vane tips and the inner surface of the cam block resulting in damage to the vane and to the cam surface resulting in reduced displacement capacity.
Typically, the vanes and the cam block are fabricated from hard and brittle material in order to compensate for wear and frictional forces encountered between the vanes and the cam block. In some rotary vane pump applications, compressive stresses caused by unequal pressures on the leading and trailing surfaces, are far greater than capabilities of known steels. For this reason, the vane and cam block are typically fabricated from extremely hard materials such as Tungsten Carbide. Such hard materials are expensive, brittle and difficult to machine.
Accordingly, it is desirable to develop a balanced vane pump using ductile low cost materials to reduce costs, provide increased durability and simplify fabrication.